One of the things that could go wrong with the fuel system is the fuel pump relay, which works like a remote switch. It takes a small amount of amperage from the ignition switch to activate the relay, which then sends to the fuel pump the larger amount of amperage needed to activate the pump. You may also need to remove the relay so that you can relieve the pressure in the fuel system. If you remove the relay and crank the engine over a few times, fuel cannot get through the system, as the fuel pump will not be activated.
Open the driver's side door to the cab.
Locate the fuse panel under the dash on the driver's side of the Impreza's fuse block. It is located under the dash, to the left of the steering column.
Reach up to feel for the fuel pump relay. The fuel pump relay is located on the outside of the fuse panel. You should be able to pull it out with your fingers, but you can use pliers if needed. The fuel pump relay has two plastic clips that hold it into its socket. The clips are attached to two plastic "buttons" on the side of the relay. Use the flashlight to find the buttons, or feel for them.
Press the plastic tabs in while pulling on the relay to remove it.